This invention relates generally to polycrystalline carbon, and, more specifically, to the conversion of polycrystalline diamonds to single crystal diamonds.
Natural diamonds were formed over eons under great pressure and temperature and have unique material properties including hardness and strength. In view of the limited supply of natural diamonds and their associated high cost, synthetic diamonds were developed for use in industrial applications wherein their strength, hardness, and thermal conductivity properties may be used to advantage without the associated high cost of natural diamonds.
Diamond is a unique form of carbon although there are other forms of carbon having similar properties and referred to as diamond-like-carbon (DLC). The single crystal forms of diamond and DLC have optimum material properties due to a lack of grain structure and grain boundaries. Diamond may be found in its polycrystalline form which includes individual small crystals joined together at grain or crystal boundaries. The crystal boundaries reduce the material properties of the diamond in a manner similar to the grain boundaries found in typical metals.
Various superalloys, including nickel based and cobalt based, are specially processed in their liquid or molten state to form single crystal metal bodies upon solidification. However, these processes may not be used for diamond production in view of the extremely high temperature and pressure requirements for diamond production.
In an unrelated development, single crystal sapphire has been obtained in a solid state transformation from polycrystalline alumina. This unique process is disclosed in U.S. Pat. No. 5,427,051, assigned to the present assignee, and uses a localized energy source to heat a portion of a polycrystalline alumina body to a temperature approaching its melting temperature for obtaining solid state conversion to sapphire. However, diamond and sapphire are different materials having different properties.
Accordingly, it is desired to transform polycrystalline diamond into single crystal diamond in a solid state process which is an improvement over the polycrystalline alumina-to-sapphire transformation process of the above patent.